Embodiments of the invention relate to wall sensors. Wall sensors include the capability of detecting, for example, wooden or metal studs hidden behind a surface. In some instances, wall sensors include one or more plate sensors or high frequency transmitters for determining whether an object is hidden behind a surface. Wall sensors also include an indicating device or multiple indicating devices for alerting a user to the presence of an object that is hidden behind a surface. Indicating devices can include visual indicators such as light emitting diodes (“LEDs”), audible indicators such as a small speaker, or a combination thereof.